TWO SPRING REGULATORY INCIDENTS
Sudden Oak Death – Infected nursery stock, Julie VanMeter, Nebraska Department of Agriculture
Nursery Stock Infected with Sudden Oak Death
Recently, a small amount of container grown rhododendron nursery stock potentially infected with Phytophthora ramorum, also known as Sudden Oak Death or SOD, was shipped to Walmarts and a Builders Warehouse in Nebraska. Inspectors with the Nebraska Department of Agriculture (NDA) along with staff from USDA Plant Protection and Quarantine, continue to follow up with these locations to minimize the threat of infected nursery stock being distributed in the state.
The nursery stock originated in Washington and Canada, and was supplied by Park Hill Plants in Oklahoma. It was shipped to numerous states in the plains, mid-west and eastern United States. USDA has identified five varieties of rhododendrons from the grower that have tested positive for SOD at this time, including Firestorm, Cat Cunningham Blush, Holden, Nova Zembla and Roseum elegans.
Nebraska is at low risk for establishment of SOD, because our climate is considered unsuitable for the pest, and the state has relatively few hosts in its natural environment. However, managed landscapes may provide a suitable microclimate where an infestation could establish.
SOD is a fungus-like disease first discovered in northwest California in the 1990s. Its current distribution within the environment is limited to costal northwest California and southern Oregon. Several nurseries in Washington have also been found infected. SOD is not established in Nebraska.
Symptoms of SOD infection vary depending on the host. Currently more than 100 plants are known hosts of SOD. Some, such as tanoaks and oaks, exhibit bleeding cankers on the tree trunk, and usually die from the infection. Other plants, including viburnums and rhododendrons, experience twig and shoot die-back, and lesions on the leaves. They rarely die, but act as a source for spores to infect other plants.
USDA regulates the movement of regulated articles, including nursery stock, firewood and Christmas trees, through a federal quarantine. NDA inspectors look for SOD when doing nursery inspections, and may ask for paperwork to confirm compliance with the quarantine when inspecting any regulated article. Five genera of nursery stock most commonly found infected with SOD, and thus considered high risk for spreading the disease, are Camellia, Kalmia, Pieris, Rhododendron (including azaleas), and Viburnum.
Nurseries in quarantined counties in California and Oregon, and regulated nurseries in Washington, must be certified by either their state departments of agriculture or USDA in order to be eligible to ship regulated materials to other states. Paperwork indicting this compliance must accompany each shipment of nursery stock. Nebraska nurseries need to maintain this paperwork and show it to inspectors when requested.
Boxwood Blight, Yonghao Li, The Connecticut Agricultural Experiment Station, Bugwood.org
BOXWOOD BLIGHT TRACE FORWARD INCIDENT
Boxwood plants from Ohio, potentially infected with boxwood blight, were shipped to a handful of nursery stock distributors in Nebraska this spring. At this time, no infected boxwood have been confirmed through follow-up inspections. Boxwood blight is a fungal disease that was first detected in the United States in 2011, in North Carolina and Connecticut. Since that time, it has been confirmed in a number of other states. Boxwood blight’s primary means of long distance travel is by infected nursery stock. Symptoms of an infection include dark spots and brown blotches on leaves, and white sporulation on the under sides of leaves. Green twigs will show black cankers, and the plant will usually defoliate rapidly.
Boxwood Blight, Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org
The fungus will overwinter on infected plants and infected leaf litter. Sanitation is the best way to manage this disease. Infected plants, including leaf litter, should be double bagged and disposed of in the trash or buried. Burning is also effective. The fungus can remain in the soil for at least five years, so planting new boxwoods into previously infected beds is not recommended. Applying fungicides prior to infection may offer some protection, but will not cure a plant already infected with boxwood blight.
To prevent bringing a plant pest like Sudden Oak Death or boxwood blight into your nursery, talk with your suppliers.
Be familiar with the known distribution of pests, and consider that information when you order material. Confirm that they are growing the nursery stock, and not brokering it from another nursery. Ask the nursery how they manage for particular plant pests.
If you suspect you’ve received nursery stock infected with SOD or boxwood blight, or any other pest, contact Julie Van Meter with the Nebraska Department of Agriculture Entomology Program at 402-471-2351.
The UNL Plant and Pest Diagnostic Clinic is also available to help diagnose plant pest problems, including SOD and boxwood blight. Contact Kyle Broderick at (402) 472-2559 or kbroderick2@unl.edu for information on how to submit samples.